Delta-9-THC, 15 mg/kg augments methamphetamine induced locomotor activity in aggregate mice. With high doses a decrease in activity took place. In humans the combined treatment of marihuana smoking to deliver 25 mcg/kg THC and D-amphetamine orally, 10 mg/kg increased heart rate additively. A similar effect was seen on systolic blood pressure. Subjective responses were more intense. D-amphetamine did not modify psychomotor impairment produced by marihuana. In humans the combined treatment of secobarbital 150 mg/kg orally and marihuana smoking to deliver 25 mcg/kg produced psychomotor impairment and subjective effects which were the sum of that produced by each alone. Animals pretreated with either CBD or THC and challenged with methaqualone experienced a lengthened methaqualone sleep time. THC effect was more pronounced. BIBLIOGRAPHIC REFERENCES: Dalton, W.S., Martz, R., Lemberger, L., Rodda, B.E., and Forney, R.B.: Clinical Effects of Marihuana Combined with Secobarbital. Clin. Parmacol. Ther. 18(3):298-304, 1975. Stone, C.J., McCoy, D.J., and Forney, R.B.: Combined Effect of Methaqualone and Two Cannabinoids. J. For. Sci. 21(1):108-111, 1976.